Abstract: Objective This study was conducted to understand the immunity in the high-risk population of penussis and diphteria in Tianjin City．Methods Eight age groups of children aged 2 to 1 7 years were sampled at random，and 1103 effective blood samples were taken．The diphteric antitoxin was determined with indirect hemaglutination(IHA)，while the antibody of pertussis with micro agglutination test，and at the same time，a statistical analysis for the monitoring results was done with SPSS 11.5．Results Among healthy people aged 2 to 17 years，the positive rate of antibody for pertussis measured with micro agglutination test was 65.29％，and protective rate 38.17％．The positive rate of antibody and GMRT decreased significantly with increase of age．The protective rates for antibody of diphtheria were a11 above 80.00％，and averaged 87.98％，with average antitoxin 0.12 IU/ml．The protective rate for antibody and average antitoxin all showed a significant difference among age groups．Conclusion Further immunization work for pertussis and diphtheria should be emphasized at the same time that immunity monitoring among healthy people is continued．